Evacuation of electronic devices



' Au 15, 1933. 7 A Km 1,922,162

EVACUATION OF ELECTRONIC DEVICES Filed Feb. 10, 1932 INVENi'QR Ade/7 I K1723 his ATTORNEY Patented Aug. 15, 1933 UNITED STATES EVACUATION OF ELECTRONIC DEVICES Aden J. King, Syracuse, N. Y., assignor to King Laboratories, Inc., Syracuse, N. Y., a Corporation of New York Application February 10,1932. Serial No. 591,967

6 Claims.

high vacuum in so-called vacuum tubes and relates more particularly to the production of high vacuum in thermionic tubes.

.The accepted methods of exhausting airfrom vacuum tubes are to evacuate the tube as thoroughly as possible by the action of pumping devices, then to seal off the tube while on the pump, and, as a final step, removing the greater part of the residual gasesby getter action. A common getter is magnesium which is supported to one of the electrodes of the tube before the sealing step. The usual method of flashing the getter is to introduce the tube into the field of a high frequency coil, the magnesium tape, or the shield, to Which it is attached, being heated by high frequency current passed through the coil to its flash temperature. On the flashing of the getter, the larger part of the residual gases is effectively removed by chemical and physical action.' The tube is then found to be suitably evacuated for operation with the usual potentials. The practice in the past has been to assemthe other of the two following methods: The magnesium getter is supported by electrically spot welding a piece of magnesium ribbon directly to one of the electrode plates, to a separate metal plate or to a metal cup, which is later attached to one of the electrodes, or electrode supports, within the tube. The disadvantages of this method are that it is not de sirable to be limited only to magnesium as a getter, and, furthermore, the magnesium ribbon must be first cut into suitable lengths, welded to its mounting plate in several places in order to get close contact, the mounting plate must be welded to a support wire, and, finally,

the support wire welded to an electrode or electrode support in the tube. With this method, much labor is involved in the large number of assembly steps and the material is exposed to the deleterious action of the, atmosphere during the prolonged assembly. This method has not been found to lend itself most effectively to large scale manufacturing. Another form of getterwhich, in certain in- 6 stances; has been found to be more effective than magnesium has been magnesium alloyed with barium, strontium, or calcium. It has been the practice to mix these materials in powdered form and to form a getter pellet which is placed in a metal container which is then welded to an electrode support within a tube. This method ble and mount the getter material in one or This invention relates to the production of has many undesirable features in that not only are there many separate steps required in the formationo'f the pellet and in the mounting of the getter within the tube, these disadvantages being substantially-the same as have been referred to in connection with the description of the magnesium ribbon getter, but due to the limited contact between the getter and its container, the heat transfer between the container and the pellet is poor, and, as a result, much higher temperatures are required for flashing or vaporizing the getter. Furthermore, due to the fact that the pellet is contained in, and shielded by, the getter cup, no direct heating of the pellet by eddy currents from the high frequency current is realized, and the vaporization of the getter is obtained only by radiation or slight heat conduction. These characteristics of the common form of getter require higher temperatures in the getter cup and require greater power in-. put to the high frequency coils, more high frequency coils, and a longer time on the bombarding machine. The high temperatures required have prevented many materials, such a cerium, mischmet'al, or other metals having high boiling points, which would effectively serve as getters, from being used, because the temperature to which the getter container must be raised before such getters reach their vaporization point, causes melting or vaporization of the container itself.

An object of this invention is to provide a getter which may be vaporized at relatively low temperatures.

Another'object of the invention is to form a getter support of which the getter is an integral part.

Another object of the invention is to provide intimate contact between a getter and its support.

Another object of the invention is to provide a. manufacturing process for the economic production of efficient getters on a quantity production basis. 7

According to this, invention, getter material in powdered form is placed on a metallic sheet, and in a later step the material is pressed directly into the support to effectively weld the getter material into the support. One satisfactory way of doing this is to pass a metallic ribbon underneath a hopper which feeds desired amounts of getter material at spaced intervals along the ribbon which then passes underneath a press which presses the material into the ribbon so that the two are pressed or welded together. The metal-.

lic sheet is later cut into sections, each section forming a getter and getter support which may be readily and quickly welded to a support within a vacuum tube.

The getter material which is preferably used is a barium-aluminum alloy which I have originated. Examples of my preferred alloys are as follows:

'1. Pure barium-aluminum--% barium.

2. barium-aluminum alloy+25% magnesium powder.

3. 50% barium-aluminum alloy+50% magnesium powder.

4. 25% barium-aluminum alloy+75% magnesium powder.

The invention will now be described with reference to the drawing, of which:

Fig. 1 is a diagrammatic view of a manufacturing method which may be used for forming a getter structure, according to this invention;

Fig. 2 is a plan view of one form of a getter structure constructed by the process of Fig. 1;

Fig. 3 is a side view, in section, of a preferred form of getter structure formed according to a process of Fig. 1, and

Fig. 4 is a view of the internal structure of a vacuum tube with the getter structure, such as shown by Fig. 2, attached to one of the electrode supports.

Referring now to Fig. 1, a metallic ribbon 5, which may be nickel, is made to pass, by the employment of any suitable apparatus, under the hopper 6, which contains the getter material '7, in powdered form and which deposits, under suitable control, the proper amount of getter material 8 at spaced intervals on the ribbon. The ribbon next passes between the two members 9 and 10 of a press. The two members 9 and 10 are pressed together, with or without the use of heat, and sufficient pressure is used to press the getter material into the surface of the ribbon and to form the indentures 11 in the base of which the pressed getter material 12 is contained. The ribbon is then cut into sections by any suitable method and each of these sections is then ready for mounting in a vacuum tube as a complete getter assembly.

Fig. 3 shows a form of getter structure which may be manufactured, according to a process of Fig. 1. In this instance, the stamp members act to form a deep cup 13 in the base of which the getter material 12 is pressed. An advantage of this form of getter structure is that the deposit of the material when vaporized is limited to the lower part of the tube.

Fig. 4 illustrates one way in which the getter structure, according to this invention, may be assembled in a vacuum tube. The getter section 14 of Fig. 2 has welded thereto the support wire 15, and this wire 15, in turn, is spot welded to the anode support 16. The elements of the tube shown by Fig. 4 are well known and, since forming no part of this invention, will not be described in detail.

It is seen that, according to this invention, the getter material is pressed into the getter shield, support, or plate, as it is variously described. The getter material is in such intimate contact with the metal sheet that its heat and electrical conductivity are high, there being no appreciable losses. As a result, when the assembled tube is placed in a high frequency coil, the heat generated in the getter support, by the action of the high frequency field, is transmitted without loss to the getter material, which, as a result, vaporizes at a relatively low temperature. This results not only in the fact that many materials which otherwise could not be utilized in getters may be effectively used, but the time required for gettering the tube is reduced and the number of bombarding stages required are reduced. Furthermore, the getter assembly may be mounted at a lower position in the tube, without loss of efficiency in flashing, so that the deposit of vaporized metal, when a getter structure such as shown by Figs. 2 and 4 is employed, does not extend an undesirable distance on the inside of the tube wall, or glass stem supporting the electrodes.

As has previously been explained, the manufacturing process illustrated diagrammatically by Fig. 1, not only produces an improved getter, but the manufacture of the getter structures is rendered simpler and less expensive. It is no longer necessary 'to form the getter into pellets, the getter material being pressed in powdered form into its supporting metal.

Any form of getter material which is now being generallyused may be utilized, according to this invention, and, as has previously been explained, many other materials not now used due to their high vaporization temperatures may now be employed.

What is claimed is:

1. The method of manufacturing a getter assembly which comprises reducing getter material to a powder, and pressing the powder into a support.

2. The method of manufacturing a getter assembly which comprises indenting a getter support, and in the same operation pressing getter material into the base of the indentation.

3. The method of producing a getter assembly which comprises reducing getter material to a powder, forming an indentation in a metallic support, and in the same operation pressing the powder into the base of the indentation.

4. The method of producing getter assemblies which comprises reducing getter material to a powder, feeding powder at spaced intervals along a metallic ribbon, pressing the powder into the ribbon, and then separating the ribbon between the spaced intervals to provide individual getter assemblies.

5. The method of producing getter assemblies which comprises feeding getter material at spaced intervals along a metallic ribbon, pressing the deposited material in each instance between a pair of dies which forms an indented portion into the base of'which the getter material is pressed, and severing the ribbon between the spaced intervals to provide individual getter assemblies.

6. The method of producing getter assemblies which comprises reducing getter material to powder, depositing the powder at spaced intervals along a metallic ribbon, pressing the powder into the ribbon so as to form an indentation in each instance in which the powder is pressed into the base thereof, and severing the ribbon between the pressed portions to provide the individual assemblies.

ADEN J. KING. 

